title: Def-6, a novel regulator of small GTPases in podocytes, acts downstream of atypical protein kinase C (aPKC) λ/ι.
abstract: The atypical protein kinase C (aPKC) isotypes PKCλ/ι and PKCζ are both expressed in podocytes; however, little is known about differences in their function. Previous studies in mice have demonstrated that podocyte-specific loss of PKCλ/ι leads to a severe glomerular phenotype, whereas mice deficient in PKCζ develop no renal phenotype. We analyzed various effects caused by PKCλ/ι and PKCζ deficiency in cultured murine podocytes. In contrast to PKCζ-deficient podocytes, PKCλ/ι-deficient podocytes exhibited a severe actin cytoskeletal phenotype, reduced cell size, decreased number of focal adhesions, and increased activation of small GTPases. Comparative microarray analysis revealed that the guanine nucleotide exchange factor Def-6 was specifically up-regulated in PKCλ/ι-deficient podocytes. In vivo Def-6 expression is significantly increased in podocytes of PKCλ/ι-deficient mice. Cultured PKCλ/ι-deficient podocytes exhibited an enhanced membrane association of Def-6, indicating enhanced activation. Overexpression of aPKCλ/ι in PKCλ/ι-deficient podocytes could reduce the membrane-associated expression of Def-6 and rescue the actin phenotype. In the present study, PKCλ/ι was identified as an important factor for actin cytoskeletal regulation in podocytes and Def-6 as a specific downstream target of PKCλ/ι that regulates the activity of small GTPases and subsequently the actin cytoskeleton of podocytes.
authors.affiliation: Division of Nephrology, Department of Medicine, Hannover Medical School, Hannover, Germany.
authors.forename: Kirstin
authors.initials: K
authors.lastname: Worthmann
authors.affiliation: Biotechnology Centre of Oslo, University of Oslo, Oslo, Norway.
authors.forename: Michael
authors.initials: M
authors.lastname: Leitges
authors.affiliation: Division of Nephrology, Department of Medicine, Hannover Medical School, Hannover, Germany.
authors.forename: Beina
authors.initials: B
authors.lastname: Teng
authors.affiliation: Faculty of Medicine, Interdisciplinary Centre for Clinical Research (IZKF) Leipzig, University of Leipzig, Leipzig, Germany.
authors.forename: Marcello
authors.initials: M
authors.lastname: Sestu
authors.affiliation: Division of Nephrology, Department of Medicine, Hannover Medical School, Hannover, Germany.
authors.forename: Irini
authors.initials: I
authors.lastname: Tossidou
authors.affiliation: Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina.
authors.forename: Thomas
authors.initials: T
authors.lastname: Samson
authors.affiliation: Division of Nephrology, Department of Medicine, Hannover Medical School, Hannover, Germany.
authors.forename: Hermann
authors.initials: H
authors.lastname: Haller
authors.affiliation: Renal Division, University Hospital Freiburg, Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-University, Freiburg, Germany.
authors.forename: Tobias B
authors.initials: TB
authors.lastname: Huber
authors.affiliation: Division of Nephrology, Department of Medicine, Hannover Medical School, Hannover, Germany. Electronic address: schiffer.mario@mh-hannover.de.
authors.forename: Mario
authors.initials: M
authors.lastname: Schiffer
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology*; D020662:Guanine Nucleotide Exchange Factors; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D050199:Podocytes / Q000166:cytology / Q000378:metabolism*; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D051744:Protein Kinase C-epsilon / Q000235:genetics / Q000378:metabolism; D000099293:Protein Kinase C-lambda
chemical_list: D004268:DNA-Binding Proteins; D020558:GTP Phosphohydrolases; D020662:Guanine Nucleotide Exchange Factors; D007527:Isoenzymes; D009687:Nuclear Proteins; D011493:Protein Kinase C; D051744:Protein Kinase C-epsilon; D000099293:Protein Kinase C-lambda; C473249:Def6 protein, mouse